Fresh air strikes pounded Syria's Aleppo city early on Monday as US Secretary of State John Kerry arrived in Geneva in a bid to halt the mounting carnage.

More than a week of fighting in and around Syria's second city has killed hundreds of civilians.

Air strikes on rebel-held east Aleppo hit in the early hours of Monday, AFP's correspondent there said, with no immediate reports of casualties.

Several neighbourhoods, including the heavily populated Bustan al-Qasr district, were hit. It was not clear if Monday's raids on the rebel area were conducted by Syrian or Russian jets.

Video footage of the aftermath of one air strike showed a distressed woman in the street, crying "My children, my children, where are they?"

A second explosion then shakes the neighbourhood.

On Monday afternoon, rebels fired rockets at western districts of Aleppo that are under government control, the Syrian Observatory for Human Rights monitor said.

Growing violence in and around Aleppo has left more than 250 civilians dead in a week and threatened both a UN-backed peace process and a fragile ceasefire deal.

Kerry arrived in Geneva on Sunday for talks with Arab ministers and UN peace envoy Staffan de Mistura in an urgent push to end the bloodshed.

"Both sides - the opposition and the regime - have contributed to this chaos," Kerry told reporters in Geneva, speaking alongside de Mistura.

"We are working over these next hours intensely in order to try and restore this cessation of hostilities."

Kerry also told reporters that he was "talking directly to the Russians, even now" despite apparent Moscow reluctance to rein in its ally, Syrian President Bashar al-Assad.

United Nations Secretary-General Ban Ki-moon on Monday also called for the ceasefire to be restored and extended to all areas of Aleppo.

Ban is "profoundly concerned about the dangerous escalation of fighting in and around Aleppo and the intolerable suffering, counted in mounting deaths and destruction, it is causing among civilians," said UN spokesman Stephane Dujarric.

The UN chief noted the re-launch of the cessation of hostilities in Damascus and Latakia and stressed "the need to expand these arrangements to other parts of Syria, with a special urgency for Aleppo".

Russian Foreign Minister Sergei Lavrov is now expected to host UN envoy Staffan de Mistura for talks on Syria in Moscow on Tuesday, the foreign ministry said.

However, the international community remains firmly divided on the crisis.

Saudi Arabia’s foreign minister, Adel al-Jubeir, who met with Kerry on Monday, strongly criticised the Syrian government and its allies.

"There is only one side that is flying airplanes, and that is Bashar al-Assad and his allies, so they are responsible for the massacre of women, children, and the elderly,” he said.

“They are responsible for the murder of doctors and medical personnel, and this situation, any way you slice it, will not stand. The world is not going to allow them to get away with this.”

The Syrian opposition, the Free Syria Army, made up of a coalition of rebel groups fighting on the ground, vowed to retaliate.

“Any attack against any liberated area where one of our factions is present will be considered an assault against all factions… and we will have a right to respond," the FSA said in a statement issued over the weekend.

Violence escalated in Aleppo late last month as UN-led talks in Geneva collapsed, with rebels firing rockets into government-held western Aleppo and Syrian government forces striking the rebel-held east in tit-for-tat air strikes. Dozens of children are among the dead on both sides.

Aleppo was initially left out of a deal to "reinforce" a 27 February truce between the government and rebels.

The freeze in fighting, announced on Friday, applied to battlefronts in the coastal province of Latakia and Eastern Ghouta, near Damascus.

The head of Moscow's coordination centre in Syria said on Sunday that talks to include Aleppo had begun.

The Syrian army announced on Monday that the "regime of calm" around Damascus had been extended for another 48 hours but made no mention of a 72-hour lull in fighting in the north of coastal province Latakia.

More than 270,000 people have been killed since Syria's conflict erupted in March 2011 with protests demanding Assad's overthrow.